Keeping a musical ensemble together for any length of time is an accomplishment. When it’s a 10 piece Improvised Music group, and the period is a quarter century, the achievement is even more remarkable. But that’s what Mood Music for Time Travellers celebrates: the 25th anniversary of the Massachusetts-based Either/Orchestra (EO). The EO’s potent mix of Jazz, Rock, Funk and more recently African influences, makes it unique among most American Jazz groups.

This sort of uniqueness is compounded, but expressed in other ways when compared to another long-established tentet, the Dutch Instant Composers Pool (ICP) Orchestra. That’s because that collection of Amsterdam’s most individualistic players has been navigating the choppy waters of Jazz and Improvised Music since 1969. Although over the years, the two bands have been training ground for players who have gone off to acclaim elsewhere, the reason both the ICP and EO remain going concerns, as these CDs demonstrate, is that many first-class players sign on for extended periods. Similarly both depend on the compositional and organizational skills of one man: saxophonist Russ Gershon in the EO’s case, and pianist Misha Mengelberg in the ICP’s. Six of the 10 compositions on the EO CD are Gershon’s; while Mengelberg is sole or co-writer of seven of 12 (049) tracks.

Because it’s part of a celebratory milestone Mood Music for Time Travellers also features guest appearances by a couple of EO alumni. However, while everyone gets proper blowing space, the nagging complaint about the CD is that no soloists are listed, a hindrance when the band has two trumpeters and three saxophonists. Otherwise the CD has few other faults.

Showing Gershon’s generosity – or sonic smarts – in fact, two of the most notable tunes, “Thirty Five” and “History Lesson”, are compositions of Rick McLaughlin, the band’s long-time bass player. Reflecting the EO’s collaborations in person and on record with different Ethiopian singers and instrumentalists, the first mixes Ethiopian modes with Jazz harmonies, while the latter salutes Nigeria’s best-known music star, Fela Kunti. With a theme expressed by every member of the band differently, high-pitched unison brass articulation, tough syncopated piano lines and slick doubled-tongued soprano saxophone lines stand out on “Thirty Five”. As for the latter piece, clanking piano runs and note clusters from Rafael Alcala, plus McLaughlin’s repetitive bass patterns set the pace, allowing space for a riffing saxophone solo from either a high-pitched baritone or mid-range tenor.

Perhaps as influenced by Duke Pearson and Duke Fakir as Duke Ellington, Gershon is an accomplished, if more funkified, composer himself. The first track, “The (One of a Kind) Shimmy”, is an unabashed boogaloo, for instance, encompassing piano chording that seems to have stepped out of “The Sidewinder”, call-and-response section work from mellow muted brass and tremolo shimmies from the composer’s soprano saxophone. Meantime, “The Petrograd Revision” takes it shape from African, Funk and the better parts of Jazz Fusion material. Melding Pablo Bencid’s back-beat drumming, a walking bass line, slapped conga drum rhythms, Alcala’s quivering organ timbres plus contrapuntal vamps from the horns, the tune ends up being simultaneously clean and funky. And there’s still room for Gershon’s exposition and a linear, graceful trumpet solo.

Funk may be absent from (049), but that’s one of the few genres upon which the band doesn’t touch. A group of individualized soloists, the ICP also has a string section – Mary Oliver’s violin and viola, Tristan Honsinger’s cello and sometimes Ernst Glerum’s arco bass – which the EO lacks. Plus with Honsinger and ICP co-founder drummer Han Bennink on board, disruptions are common along with unexpected musical avenues which suddenly leading to more exploration.

Consider “Busy Beaver”, for instance. Sounding for all intents and purposes like a jolly march perfect to be played by a European street band, the tune turns out to be a composition by pianist Herbie Nichols. Re-imagined by reedist Ab Baars, the performance includes trombonist Wolter Wierbos’ bell wiggles and plunger work, altered sul ponticello from the cellist that’s harmonized with Glerum’s ostinato and pops, plus slaps and rebounds from Bennink.

Mengelberg’s own “No Idea’, also takes on many shapes in an arrangement by reedist Michael Moore. At points an atmospheric ballad, the string section appears to be channeling mood music of the 1950s, as the horns riff harmonically and the composer plinks out Errol Garner-styled runs. Meanwhile on the other side of the bandstand, trumpeter Thomas Herberer’s half-valve effects seemingly exist on a different plane than the trombonist’s pedal point. Plus Bennink insists on steadily increasing clatters and bangs, as if he was Sonny Greer goosing an Ellington killer-diller.

At the same time the CD – which also includes a DVD track linking Amsterdam visuals to a jokey, swinging band improvisation – is studded with other musical references as well. The pianist spends one track mumbling to himself in Dutch – or is it double Dutch? – and another showing off his Monk-like chops. Honsinger and tenor saxophonist Toby Delius combine for one number that posits what would happen if cello lines were added to an R&B-like saxophone showcase. Additionally, Baars showcases mellow clarinet vibrations during his arrangement of Ellington’s “Sonnet in Search of a Moor”. Baars’ solo may be strictly in mid-1950s Jimmy Hamilton mode, but Glerum’s solid walking and string-popping suggests that of Wellman Braud, a ducal bassist from a much earlier Ellington epoch.

Perhaps this thoughtful mélange of styles frequently demonstrated is one reason for the long-term existence of both the American and the Dutch groups. Changing a slogan slightly to “if it sounds good, do it”, the ICP and EO apparently follow that dictum. By also adding unique elements that result from the players’ individual skills, both can create exceptional CDs.